16.4. Accessing an EJB from a Servlet or JSP Page
Starting with JOnAS 2.6 with its web container service, it is possible to access an enterprise Java bean and its environment in a J2EE-compliant way.
The following sections describe:
How to access the Remote Home interface of a bean.
How to access the Local Home interface of a bean.
How to access the environment of a bean.
How to start transactions in servlets.
 | Note |
|---|---|
All the following code examples are taken from the The EarSample example provided in the JOnAS distribution. |
16.4.1. Accessing the Remote Home Interface of a Bean:
In this example the servlet gets the Remote Home interface OpHome registered in JNDI using an EJB reference, then creates a new instance of the Session Bean:
import javax.naming.Context;
import javax.naming.InitialContext;
//remote interface
import org.objectweb.earsample.beans.secusb.Op;
import org.objectweb.earsample.beans.secusb.OpHome;
Context initialContext = null;
try {
initialContext = new InitialContext();
} catch (Exception e) {
out.print("<li>Cannot get initial context for JNDI: ");
out.println(e + "</li>");
return;
}
// Connecting to OpHome through JNDI
OpHome opHome = null;
try {
opHome = (OpHome)
PortableRemoteObject.narrow(initialContext.lookup \
("java:comp/env/ejb/Op"), OpHome.class);
} catch (Exception e) {
out.println("<li>Cannot lookup java:comp/env/ejb/Op: "
+ e + "</li>");
return;
}
// OpBean creation
Op op = null;
try {
op = opHome.create("User1");
} catch (Exception e) {
out.println("<li>Cannot create OpBean: " + e + "</li>");
return;
} |
Note that the following elements must be set in the web.xml file tied to this web application:
<ejb-ref> <ejb-ref-name>ejb/Op</ejb-ref-name> <ejb-ref-type>Session</ejb-ref-type> <home>org.objectweb.earsample.beans.secusb.OpHome</home> <remote>org.objectweb.earsample.beans.secusb.Op</remote> <ejb-link>secusb.jar#Op</ejb-link> </ejb-ref> |
16.4.2. Accessing the Local Home of a Bean:
The following example shows how to obtain a local home interface OpLocalHome using an EJB local reference:
//local interfaces
import org.objectweb.earsample.beans.secusb.OpLocal;
import org.objectweb.earsample.beans.secusb.OpLocalHome;
// Connecting to OpLocalHome thru JNDI
OpLocalHome opLocalHome = null;
try {
opLocalHome = (OpLocalHome)
initialContext.lookup("java:comp/env/ejb/OpLocal");
} catch (Exception e) {
out.println("<li>Cannot lookup java:comp/env/ejb/OpLocal: "
+ e + "</li>");
return;
} |
This is found in the web.xml file:
<ejb-local-ref>
<ejb-ref-name>ejb/OpLocal</ejb-ref-name>
<ejb-ref-type>Session</ejb-ref-type>
<local-home>org.objectweb.earsample.beans.secusb.OpLocalHome
</local-home>
<local>org.objectweb.earsample.beans.secusb.OpLocal</local>
<ejb-link>secusb.jar#Op</ejb-link>
</ejb-local-ref> |
16.4.3. Accessing the Environment of the Component
In this example, the servlet seeks to access the component's environment:
String envEntry = null;
try {
envEntry = (String)
initialContext.lookup("java:comp/env/envEntryString");
} catch (Exception e) {
out.println("<li>Cannot get env-entry on JNDI " + e + "</li>");
return;
} |
This is the corresponding part of the web.xml file:
<env-entry> <env-entry-name>envEntryString</env-entry-name> <env-entry-value>This is a string from env-entry</env-entry-value> <env-entry-type>java.lang.String</env-entry-type> </env-entry> |
16.4.4. Starting Transactions in Servlets
The servlet wants to start transactions via the UserTransaction:
import javax.transaction.UserTransaction;
// We want to start transactions from client: get UserTransaction
UserTransaction utx = null;
try {
utx = (UserTransaction)
initialContext.lookup("java:comp/UserTransaction");
} catch (Exception e) {
out.println("<li>Cannot lookup java:comp/UserTransaction: "
+ e + "</li>");
return;
}
try {
utx.begin();
opLocal.buy(10);
opLocal.buy(20);
utx.commit();
} catch (Exception e) {
out.println("<li>exception during 1st Tx: " + e + "</li>");
return;
} |